1. Field of the Invention
The present invention relates to a fuel pump that has a pump housing and an inlet port at a side of the pump housing.
2. Description of the Related Art
A fuel pump that has a pump housing, a pump passage having an inlet port, a motor and an impeller housed in the pump housing is well-known for pressurizing fuel in the pump passage, as disclosed in U.S. Pat. No. 6,942,447 B2 or JP-A-2004-100675 that is a counter part of the U.S. patent.
In the above fuel pump, the inlet port is opened at a circumferential side of the pump housing or the impeller to take fuel into the pump passage formed along the periphery of the impeller. Therefore, the fuel intake resistance of this type is smaller than another type of fuel pump that has an inlet port opened in the direction perpendicular to the rotation direction of the impeller. That is, the pump efficiency of the former fuel pump is higher than the latter fuel pump.
Incidentally, the pump efficiency Peff is expressed as follows:
Peff=(P×Q)/(T×N), wherein: T is a torque of the motor; N is a rotation speed of the motor; P is a pressure of fuel; and Q is a quantity of fuel discharged from the pump.
If the fuel intake resistance is reduced, the quantity of fuel to be discharged by the pump increases, and the pump efficiency increases.
FIG. 5 shows a fuel pump in which an inlet port 212 of a pump passage 210 is formed on a side of a pump housing 200. In the fuel pump, an intake resistance is generated when fuel is taken from portions around the inlet port 212 into the pump passage 210. In particular, the streamlines of the fuel flow peel off when the direction of the fuel flow sharply changes at an edge 214 of the inlet port 212. Accordingly, the effective sectional area of the fuel passage for taking fuel into the pump passage 210 reduces, resulting in that the fuel intake resistance increases to thereby reduce the pump efficiency.